Outdoor wood-burning boilers typically include air supply tubes that carry air from a fan or pump into the interior of the wood-burning enclosure. When there is no need for air to be pumped into the boiler, for example, when the temperature of water to be heated by the boiler is sufficiently high, exhaust smoke from the burning wood seeps into the air supply tubes and fouls them. The smoke and other unburned combustion products, including creosote, can coat the insides of the air supply tubes, reducing the efficiency of the boiler and posing an inner-tube fire risk. Cleaning the air supply tubes requires ceasing operation of the boiler, cooling the boiler, and disassembly of the boiler. A need exists for an outdoor wood-burning boiler that includes an air supply system that can be easily cleaned without the need to stop operation of and cool down the boiler.